1. Technical Field
The present invention relates to a current sensor used for measuring a current flowing through a current path and a method for manufacturing the current sensor.
2. Background Art
In order to measure a current of a battery mounted on a vehicle or a current to be supplied to a motor, a current sensor which is provided with a magnetic detection element such as a hall element and a magnetic shield core, detects magnetism produced from a current path such as a bus bar, and measures a current flowing through a current path has been used (see JP-A-2010-223868, JP-A-2010-2277 and JP-B-4515855, for example)
In this context, flowing of a large current (600 A, for example) through a current path such as a bus bar has been studied as electrical vehicles and the like have widely been distributed in recent years.
In order to detect such a current flowing through the current path, a current sensor with a structure in which a magnetic shield core 500 extending around the current path 600 is used to detect magnetism by a magnetic detection element 400 as illustrated in FIGS. 10A and 10B can be considered. If it is attempted to measure the current of the current path 600, through which a large current is made to flow, by the current sensor, a current value measured by the current sensor becomes smaller than an actual current value, and a relationship between the current value measured by the current sensor and the actual current value cannot maintain linearity. This is because the magnetic shield core 500 cannot sufficiently converge a magnetic flux produced from the current path 600 at a gap portion 510 and a so-called magnetically saturated state occurs at the core portion.
As countermeasures for the magnetic saturation at the core portion, the following two countermeasures can be considered.
(1) Density of a magnetic flux (a magnetic flux per unit area) converged by the core portion is reduced by increasing a width of the core portion to increase areas of end surfaces of the core portion, which face each other at the gap portion.
(2) Density of a magnetic flux converged by the core portion is reduced by widening the gap portion of the core portion to increase the interval between the two end surfaces of the core portion, which face each other at the gap portion, and to increase resistance at the gap portion.
However, the aforementioned countermeasure (1) has a problem in that the size of the magnetic shield core increases, and the aforementioned countermeasure (2) has another problem in that magnetic field noise, which flies from the outside to the current sensor and is not a target of detection, has a greater influence.
In order to solve such problems, a current sensor provided with a magnetic shield core 500 formed in a U shape as illustrated in FIG. 11 can be considered. According to the current sensor, the current flowing through the current path 600 concentrates on both sides of the bus bar, which corresponds to the current path 600, in the width direction. Then, a magnetic flux produced from the current flowing on both sides of the current path 600, as a generation source, becomes dominant in the magnetic flux detected by the magnetic detection element 400. If a distance between the generation source and the magnetic detection element 400 increases, a phase difference is generated between a magnetic field produced from the generation source and a magnetic field which reaches the magnetic detection element 400. For this reason, the magnetic flux detected by the magnetic detection element 400 is delayed relative to the current flowing through the current path 600, and accordingly, responsiveness of the current sensor deteriorates.